Beta-lactam antibiotics are nowadays frequently used for chemotherapy of infectious diseases. However, cephalosporin antibiotics and penicillin antibiotics, both beta-lactam antibiotics, are degraded by cephalosporinases and penicillinases, respectively, and consequently loose their antibacterial activity. For this reason, treatment by beta-lactam antibiotics can not be expected to have the desired effect as the infection-causing bacteria in a patient are beta-lactamase producing bacteria. In choosing a drug for the treatment of an infectious disease, it is thus important to judge beforehand whether or not infection-causing bacteria are beta-lactamase producing bacteria.
The detection of a beta-lactamase has been so far carried out by combined detection using a penicillinase testing agent comprising a penicillin antibiotic as a substrate together with a pH indicator as well as a cephalosporinase testing agent comprising a cephalosporin antibiotic and a pH indicator. In these testing agents, the substrate for an enzyme, i.e., a penicillin antibiotic and a cephalosporin antibiotic, is hydrolyzed to afford an acid where the bacteria tested are penicillinase producing bacteria and cephalosporinase producing bacteria, respectively, and as a result, a pH indicator contained in the testing agent will change its color. Consequently, the bacteria tested are judged to be bacteria which produce both penicillinase and cephalosporinase, where they are found as positive by each testing agent.
In general, penicillinases specifically hydrolyze penicillin antibiotics, and cephalosporinases specifically hydrolyze cephalosporin antibiotics. However, some penicillinases are known to hydrolyze not only penicillin antibiotics but also cephalosporin antibiotics as substrates. If such cephalosporinase-active penicillinase producing bacteria are subjected to the judgment according to the method described above, they will be found positive by each testing agent. As a result, bacteria producing a beta-lactamase actually classified as a penicillinase will be misjudged as bacteria producing both penicillinase and cephalosporinase. Such misjudgments sometimes lead to an improper choice of the chemotherapeutic in clinical treatment.
Accordingly, an object of the present invention is to provide a beta-lactamase testing agent which enables a proper and easy judgment of the type of beta-lactamase with no possibility of a misjudgment. In particular, its object is to provide a cephalosporinase testing agent which avoids a misjudgment on a cephalosporinase-active penicillinase that degenerates cephalosporin antibiotics. The inventors of the present invention have conducted various research, and as a result, they found that the above objects can be attained by providing a cephalosporinase testing agent which is added with a penicillinase inhibitor in addition to a cephalosporin antibiotic as a substrate for the enzyme for the detection of a cephalosporinase.